This invention relates to a method of transmitting data blocks from at least two radio base stations employing macrodiversity over at least two diversity links to a central station.
Furthermore, the invention relates to a data frame, a mobile radio system, a central station, and a base station for carrying out the method.
There are mobile radio systems with base stations which receive radio signals from a mobile station in parallel over different radio paths and which forward the user data contained in the radio signal to a central station. At the receiver of the central station, the erroneous user data received over one of the radio paths can be replaced with user data received correctly over another radio path. In other words, the user data are transmitted in parallel over separate diversity links in order to obtain at the receiving end as many correct user data as possible, i.e., to achieve the highest possible diversity gain.
In this connection, the document with the designation xe2x80x9cTS 25.427, V 0.2.1xe2x80x9d should be mentioned, which is part of the technical specification of the future mobile radio system UMTS (universal mobile telecommunications system), and which was published by the standardization body 3 GPP (3rd Generation Patnership Project) under the title xe2x80x9cUTRAN Iub/Iur Interface User Plane Protocol for DCH Data Streamsxe2x80x9d on the home page xe2x80x9chttp://www.3gpp.orgxe2x80x9d in June 1999. Chapter 7 of that document describes a method of transmitting data blocks, namely so-called transport blocks, which contain user data and are transmitted from base stations, the so-called Nodes B, to a central station, the so-called Radio Network Controller, RCN. As described in Chapter 7 with reference to FIG. 1 and Table 1, the data blocks are inserted into a data frame, with each data block being preceded by an associated check field, the so-called checksum indicator. The contents of the check field indicate whether the subsequent data block is correct or not. The base stations transmit the-data blocks in parallel over different diversity links to the central station, which then analyzes the check fields for each diversity link and which replaces an erroneous data block received over one diversity link with a corresponding correct data block received over another diversity link. Accordingly, that 3 GPP document describes a method of transmitting data blocks from at least two base stations employing macrodiversity over at least two diversity links to a central station wherein each of the base stations transmits the data blocks together with check fields within data frames to the central station, with each of the data blocks being assigned one of the check fields, wherein the central station analyzes the check fields for each of the diversity links to identify those data blocks which were correctly received, and wherein the central station replaces erroneous data blocks received over one of the diversity links with correct data blocks received over another one of the diversity links. Besides the method and the structure of the data frame, the 3 GPP document describes a mobile radio system, a central station, and a base station for carrying out the method.
The invention is predicated on recognition that, if the prior-art method is carried out using the conventional data frame structure, each data frame must be read in its entire length, i.e., from the first to the last bit, to find the individual check fields. Particular difficulties are caused during the read operation by the arrangement of the check fields, which results in the beginning of each data block being shifted backward by one bit, namely by the length of the preceding check field. Accordingly, reading the data blocks using byte-oriented addressing is not possible, and the data processing speed is reduced.
Starting from this recognition, the invention has for its object to improve the method referred to at the beginning and propose a newly structured data frame in order to expedite the analysis of the check fields and the access to the data blocks. Furthermore, a mobile radio system for carrying out the improved method, a central station, and a base station are to be provided.
The object is attained by a method of transmitting data blocks from at least two radio base stations employing macrodiversity over at least two diversity links to a central station, comprising: transmitting the data blocks from the base stations to the central station together with check fields within data frames, with each of the data blocks being assigned one of the check fields; analyzing the check fields for each of the diversity links at the central station to identify those data blocks which were correctly received; and replacing, at the central station, erroneous data blocks received over one of the diversity links with correct data blocks received over another one of the diversity links, characterized in that in each data frame, the data blocks are arranged immediately side by side, with each data block containing a number of bits divisible by 8, and that each data frame contains a check block into which the check fields are inserted and by a data frame, a mobile radio system, a central station, and a base station.
Accordingly, it is proposed to arrange the data blocks in each data frame immediately side by side, with each data block containing a number of bits divisible by 8, and to write the bits of the check fields together into a check block provided therefor. Thus, use is made of a data frame with a new structure that is characterized by an immediate succession of data blocks each comprising one byte or a multiple thereof. This results in a byte oriented structure which permits fast access to individual data blocks. With the data frame structure according to the invention and the novel method adapted thereto, a substantial increase in the speed of the digital signal processing in the receiver at the center is achieved.
Further advantageous features of the invention are apparent from the subclaims.
Particularly advantageously, each of the check fields contains at least one bit, and all bits of the check fields are written into the cheek block together, with the check block being filled with padding bits if necessary, so that the check block, too, contains a number of bits divisible by 8. This allows the check block to be addressed as a whole and to be read at a high rate.
It is also particularly advantageous to form for each data frame a check word from the bits of the check fields, to compare the check word with a first reference word for one of the diversity links in order to detect an erroneous data block received over this diversity link, and to subsequently compare the corresponding check word with a second reference word for another one of the diversity links in order to determine whether the corresponding data block was correctly received over this diversity link. Through these measures, only as many check words as necessary are analyzed and the correct data blocks are collected in a very short time by selective access.
In this connection it is particularly advantageous to produce a first result by ANDing the check word with the first reference word, to obtain a first intermediate value by ORing this first result with the negated first reference word, and to obtain the second reference word by negating this first intermediate value.
If at least one erroneous data block cannot be replaced with a corresponding correct data block, a particular advantage accrues if the process is terminated after expiration of a predeterminable period of time.